1. Field of the Invention
This invention relates to a freezing method and apparatus for freezing samples by solidifying liquid or fluid materials contained in the samples and more particularly, to a freezing which comprises a means for extending the region of a sample in which it is amorphously solidified.
2. Description of the Prior Art
When samples containing liquids therein, e.g. organism samples, are observed through electron microscope, it is the ususal practice to solidify the sample by quick freezing.
A typical apparatus of the above type is one shown in FIG. 3. In this apparatus, a sample 19 to be frozen is attached to the tip of a plunger 16. The sample 19 is manually, rapidly moved toward a pure copper block 18, which is placed in a Dewar 17 filled with a liquid helium refrigerant 20, until the surface of the sample 19 contacts the surface of the copper block 18. As a consequence, the heat energy of the sample 19 is absorbed by the copper block 18, facilitating quick freezing.
When the sample 19 containing a liquid is frozen, the tissue of the sample 19 is broken by the growth of ice crystals of the liquid. In order to freeze the sample 19 in such a state as it is, it is essential to suppress formation of ice crystals. In this regard, the known apparatus has been so designed that the copper block 18 is cooled to a very low temperature of about 10.degree. K. so that the sample 19 is cooled at a rate as fast as possible. By this, the growth of ice crystals in the sample 19 is minimized, so that the water contained in the sample 19 is solidified in the form of amorphous ice, permitting the sample 19 to be kept as it is.
However, a above known quenching apparatus has the problem that the distance where water contained in the sample 19 is amorphously frozen is limited only to part of the sample 19 at approximately 20 um from its surface which contact the copper block 18.
For high freezing rates, use of liquid helium as a refrigerant is essential which makes it difficult to handle the apparatus because of additional operation costs. This is one of the great reasons for preventing the spread of freezesolidifying techniques.